Induction motor protective circuit breaker unit

Abstract

A molded case circuit breaker unit having an accessory compartment within the circuit breaker cover, contains a field-replaceable fuse within the compartment for protecting an electric motor without tripping upon motor current reversal. Upon the occurrence of a short circuit within the protected circuit, the fuse operates to isolate the protected equipment and is conveniently replaced without disassembling the circuit breaker components.

We claim: 
     
       1. A motor-protective circuit breaker comprising: a molded plastic case and cover;   operating means within said case for interrupting circuit current upon the occurrence of an overcurrent condition within a protected electric circuit;   an electronic trip unit within said cover determining occurrence of an overcurrent condition and instructing said operating means when said condition is exceeded; and   a fuse in electric circuit with said electronic trip unit and with an electric motor, said fuse becoming operational to interrupt circuit current upon occurrence of a short circuit overcurrent condition within said protected circuit, said fuse being sized to resist melting at a circuit current value equal to or greater than fifty five percent reversal current through said motor.   
     
     
       2. The motor-protective circuit breaker of claim 1 wherein said fuse is mounted within an enclosure attached to said circuit breaker case. 
     
     
       3. The motor-protective circuit breaker of claim 1 further including an electric motor in circuit with said circuit breaker and said fuse. 
     
     
       4. The motor-protective circuit breaker of claim 1 wherein said circuit current remains uninterrupted upon occurrence of said reversal current.